If you remember the idea of resonance energy you might expect that the availability of 3 different structures with the same energy allows resonance between the structures, so that each bond is actually 4/3 of a bond, and the molecule is much more stable because of the resonance energy.

However, there is no difference between the O atoms, so how would we choose which one gets the double bond? We could put it in any position, giving 3 different structures with the same energy. This suggests that there should be 1 short bond and 2 long bonds in nitrate ion. We have to draw 1 double bond and 2 single bonds between N and O to give N exactly 8 electrons. Let's think about Lewis structures for the nitrate ion, NO 3 –.

However, it becomes very confusing in cases of multiple bond resonance! Ethylene (C 2H 4) shown (top to bottom) as a Lewis dot structure, using 'bent bonds' and sp 3 hybridization, and using σ and π bonds with sp 2 hybridization (σ and π bonding orbitals shown separate, then combined). This isn't a bad way to think for some molecules. This actually matches Lewis' image of the tetrahedra pretty well! So we could think about multiple bonds being made with hybrid orbitals just in the way that Lewis pictured, which are now called 'bent bonds' because the electron density doesn't seem to be on the line between the nuclei. In the previous section, we used hybrid orbitals to show how we can make bonds using overlapping orbitals. This turns out to match the data from crystal structures. Lewis' idea of multiple bonds suggests that they should be shorter than single bonds (because the tetrahedra share an edge or a face, not just a point). You already know that sometimes we have to use multiple bonds (double or triple bonds) to draw good Lewis structures. Predict hybridization and numbers of σ and π bonds.Define multiple bonds (name, characteristics).

The twisted bonds